The RPM trans uses its own top shaft, you cannot use any other top shaft.
With the RPM trans, you will have to use the B3/T3 slipper.
Scroll down the pages to see the exploded view of the T3.
https://www.teamassociated.com/pdf/cars_and_trucks/RC10T3/Team/cat_rtrT3.PDF
The B3/T3 has a larger diameter slipper than the original RC10,
I am using the B3/T3 slipper on my 6.5T brushless runner.
If you want to use the B4/T4 top shaft and slipper you will need to use the Stealth Gearbox.
Cheers, Dave.
